This invention relates generally to chair control mechanisms, and more particularly to a mechanism that allows the horizontal fore-to-aft position of a chair seat to be adjusted relative to the back of the seat back.
Typical office chairs and the like may have an adjustment mechanism for permitting horizontal fore-to-aft adjustment of a seat. Such mechanisms generally include guide channels or tracks attached to the seat or base within which bearing members, such as depending rods or runners, are received to permit horizontal fore-to-aft movement of the seat relative to the seat back. Often the front edge of the seat, or a front or side lever, must be raised or depressed to permit such movement. A protruding member is typically provided which engages a particular hole or indentation in the guide channel to prevent movement upon release of the seat or lever.
Chairs employing constructions such as these suffer from a number of drawbacks. For instance, such mechanisms typically include a number of parts which individually must be machined and assembled. This leads to increased cost of manufacture and assembly. Additionally, such mechanisms are often bulky and increase the overall height of the seat such that it cannot be adjusted low enough to the ground to accommodate those in the lower height percentiles of the population. Furthermore, prior art mechanisms may be equipped with one or more levers or adjustment knobs that can clutter valuable space under the chair.
Another typical office chair is designed to be self adjusting when the user shifts his or her weight. These designs use a detent and notch arrangement to adjust the fore-to-aft movement of the seat relative to the seat back. A detent is typically provided which engages a particular recess or notch to prevent movement when the user is seated and disengages when the user removes his or her weight from the seat.
Chairs employing constructions such as these also suffer from a number of drawbacks. For instance, the detent and notch arrangement allows for a substantial amount of side-to-side movement. Further, chairs employing these constructions require the user to stand up or unweight the chair allowing the detent to disengage from the notch before the fore-to-aft movement may take place. Still further, with the detent and notch arrangement, the detent may also disengage due to the partial removal of weight from the seat when a user reclines the chair. This results in unwanted movement of the chair from the fore-to-aft position.
Accordingly, there remains a need in the adjustable chair industry for a horizontal adjustment mechanism which is relatively simple, compact, and inexpensive to manufacture and assemble, which is capable of adjustment while the user is sitting, which is capable of accommodating individuals falling outside height norms, and which changes the height of the chair seat only nominally upon assembly.